My mistake: I remembered that SL only loaded up the 32 bit kernel, but it looks like it always had a 64 bit EFI. Sorry about the confusion—disregard below.

For kicks, I just ran the following terminal command on my MBP 3,1 2.2 w/ Lion installed (10.7.2)

ioreg -l -p IODeviceTree | grep firmware-abi

I expected to get back EFI32, but here is my result:

| | "firmware-abi" = <"EFI64">

I haven't seen any reference to the Santa Rosa based Macs being upgraded to a 64-bit EFI w/ Lion (and I have trolled around a bit), so I am not sure if this is news. I figured I would post it here to see if it is common knowledge.

Regardless, I figured the lack of a 64-bit EFI would limit the ability of this generation to run 10.8 when released—if this is true, it doesn't look like that will be a limitation.

When running Snow Leopard, My Mid-2007 MacBookPro 3,1 would not boot into 64 bit Kernel under 10.6 Snow Leopard. I believe I read that it was to do with a graphics driver, but I cannot quote the source at the moment.

When I upgraded to 10.7 Lion, I discovered that it does boot into 64 bit Kernel without issue.

The machine has an official limit of 4GB RAM, although Other World Computing have an unofficial 6GB upgrade kit available.

Some users have installed 8GB in this model, but with only 6GB being addressable. (Some later 4,1 models were reported to run slower with 8GB until an EFI fix came out). Since the machine can now boot into 64 bit Kernel under Lion, it would be interesting to understand whether the whole 8GB is addressable.

I know this thread is a little dated, but I've yet to come across any threads with anyone running or trying 8GB under 10.7 & 10.8, so I figured I'd share some experience.

I'll start off by saying no…8GB does not seem to run correctly under Mountain Lion (and presumably Lion), as I've considered my experience / test to be unsuccessful. Details below.

As mentioned, the MBP 3,1 has both EFI64 and 64-bit kernel in both Mountain Lion and Lion. I decided to give 8GB a try (up from 4GB) in 10.8.4. Upon initial boot, my system recognized the 8GB (Crucial brand - 8192MB total) without any problems.

Everything seems normal upon initial booting. Opening applications are also normal, with no real change in experience or performance. While continuing to open apps, I found the system fans would start to rise. This is when things became strange… As suggested by others running Snow Leopard, the system would come to a hard crawl reaching the 3GB - 4GB mark. In Activity Monitor, CPU usage would also skyrocket (around 90-99%). This was never the case with 4GB installed and half the memory utilized.

At this point, tying to use applications, move windows and access menu items were a drag. Though despite the crawling performance, applications would continue to load...VERY SLOWLY. While monitoring the system's performance through Activity Monitor, I managed to use about 5GB before deciding to force quit all apps. Once all applications were closed, the fans would return to normal.

So yes, unfortunately, it appears that stability issues continue into Lion and Mountain Lion. I would assume this is still the case with any Santa Rosa Mac. Either hardware or software limitations are to blame (or both.) As it turns out, Apple hasn't updated the EFI (currently 1.5.1) since 2008! In other thread, it is noted that Apple appears to have done 'something' to recognize the system as fully 64 in 10.7: https://discussions.apple.com/thread...art=0&tstart=0

Despite Apple making some kind of modifications to Lion and Mountain Lion to have the EFI read as 64-bit and load with a 64-bit kernel, the ability to utilize all 8GB normally has yet be the case. IMO, this begs the question why the system is able to boot and recognize all of the memory if it's not correctly supported.

With the system into it's 6th year, I wouldn't expect Apple to unlock it's full potential for 8GB (if it ever could) going into Mavericks. Funny that this system is still supported after all these years… (a real trooper if you ask! )

I've since removed a 4GB stick and replaced it with an older 2GB module for a total of 6GB. No problems as expected.

Not being able to use 8GB is a chipset limitation, not an EFI one. Some Macs with EFI limitations are the early 2006 Intell Macs, like the MacMini1,1. It can only see and use 2GB. But its chipset and the identical MacMini2,1 can see 4GB and use 3.3GB, the maximum for its 32-bit system. Once a MacMini1,1 is flashed with the 2,1 firmware, the 2GB is removed. Santa Rosa Macs have a hardware limitation. The run out of memory registers to be able to access all 8GB of ram. This happens with the 7,1/8,1 iMac, the Santa Rosa Macbooks and Macbook Pros. It wasn't until the late 2008 Macbook with the Nvidia chipset that allowed Macs (excluding the Mac Pro) to access more than 6GB of ram.

Apple has no need or reason to update the EFI on a stable older system. There's nothing Apple can to that will enable to machine to access 8GB of ram, save a hardware swap. Apple did no modifications to the EFI for 10.7+ to see it as 64-bit, it's always been 64-bit. Apple allows the system to boot with 8GB because the system is able to see it, but not use it. Just like the 3.3GB limit with older Intell Macs. Why let it boot with 4GB installed if it isn't going to use it?

Not being able to use 8GB is a chipset limitation, not an EFI one. Some Macs with EFI limitations are the early 2006 Intell Macs, like the MacMini1,1. It can only see and use 2GB. But its chipset and the identical MacMini2,1 can see 4GB and use 3.3GB, the maximum for its 32-bit system. Once a MacMini1,1 is flashed with the 2,1 firmware, the 2GB is removed. Santa Rosa Macs have a hardware limitation. The run out of memory registers to be able to access all 8GB of ram. This happens with the 7,1/8,1 iMac, the Santa Rosa Macbooks and Macbook Pros. It wasn't until the late 2008 Macbook with the Nvidia chipset that allowed Macs (excluding the Mac Pro) to access more than 6GB of ram.

Apple has no need or reason to update the EFI on a stable older system. There's nothing Apple can to that will enable to machine to access 8GB of ram, save a hardware swap. Apple did no modifications to the EFI for 10.7+ to see it as 64-bit, it's always been 64-bit. Apple allows the system to boot with 8GB because the system is able to see it, but not use it. Just like the 3.3GB limit with older Intell Macs. Why let it boot with 4GB installed if it isn't going to use it?

Apologies on the EFI, as it was always 64.

Perhaps one would think the system would safely ignore the additional 2GB if 8GB were installed.